This invention relates to urinary catheters and catheter systems generally, and more specifically to such catheters and other devices which are coated with metal to reduce microbial infection.
Four million urinary catheters are used yearly in the United States, and about 40 percent of patients develop uninary tract infections due to the use of the catheter. About 3.2 percent of the total number develop bacteriaemia (bacteria in the blood). Ten to twenty thousand people die each year, and about one billion dollars are expended to manage the complications arising from the use of urinary catheters and drainage systems. Clearly, any means which helps to reduce such infections may have a significant effect on the overall cost of medical services.
U.S. Pat. No. 3,598,127, issued Aug. 10, 1971 to Wepsic describes a catheter in which V-shaped grooves or chambers are provided, which contain antibacterial agents which diffuse through a permeable outer coating. Other patents such as U.S. Pat. No. 4,612,337, issued Sep. 16, 1986 to Fox, Jr. et al. describe various schemes for attaching or bonding antimicrobial agents to catheter materials. In general, such antimicrobial agents have a short half-life, and the microbes develop resistance to the agent.
U.S. Pat. No. 4,054,139, issued Oct. 18, 1977 to Crossley describes a catheter which embeds particles of "oligodynamic" (effective in small quantities) metals in a plastic matrix on the inner and outer surfaces of the catheter, to thereby inhibit microbial action. The matrix covers most of the surface of those metal particles and may envelop other particles completely. This arrangement, when used in a blood vessel, may produce an effect in preventing actual colonization of the surface by microbes, but may not be sufficient to kill or inhibit microbes migrating along the space between the exterior of the catheter and the skin, because of insufficient oligodynamic ion density, even though the space between the outside of the catheter and the skin which is available for migration of microbes is very small. However, the relatively large lumen required for use as a urinary catheter renders an arrangement such as that of Crossley essentially ineffective, for reasons described below.
U.S. Pat. No. 4,411,648, issued Oct. 25, 1983 in the name of Davis et al. describes an arrangement which uses an external voltage source to drive ions from a metal wire into fluid in the lumen of a urinary catheter. The ions then diffuse into the bladder. No attempt is made to prevent bacteria from moving along the outside of the catheter toward the bladder. The Davis et al. arrangement acts on bacteria or microbes moving in reflux from the exterior through the lumen, and also on those which are exiting from the bladder through the lumen.
U.S. Pat. No. 4,569,673, issued Feb. 11, 1986 in the name of Tesi, shows a pair of metal rings affixed on the exterior of a urinary catheter, with the rings connected to an external power source, for reducing microbial migration along the exterior of the catheter. Contamination through the lumen, as for example due to reflux, is not taken into account, nor is the possibility that, if microbes enter the bladder, they can colonize the exterior of the catheter at locations more distal than the rings.
All of the above patents describe devices which have metallic surfaces which are hydrophilic, and which confer protection against encrustation by proteins and minerals. Plastics are generally hydrophobic, thereby tending to increase the adhesion of bacteria and proteins.
U.S. Pat. No. 4,923,450 to Maeda, et al. describes a polymeric catheter into which silver-containing zeolite is impregnated as an antimicrobial. However, impregnation with zeolite decreases the tensile strength of the catheter.
A copending application entitled "Metallic-Surface Antimicrobial, Antithrombogenic Devices", filed concurrently herewith in the name of DeLaurentis et al., describes catheters, artificial blood vessel, valves or stents which are made from a combination of dissimilar metals which provide both antimicrobial and antithrombogenic properties. A catheter according to an aspect of the invention described in the DeLaurentis et al. application provides a conduit for access between a blood vessel or vas and the exterior of the body. The catheter includes a flexible tube which defines at least inner and outer surfaces. A layer or coating of a first metal (a metallization), supported by one or both of the inner or outer surfaces of the catheter, extends from near the point of entry into the vas to the distal end of the catheter. A coating of a second metal, dissimilar from the first metal, is supported by the same one of the inner or outer surfaces that supports the coating of the first metal. The coating of the second metal is contiguous with, and in galvanic contact with the coating of the first metal, thereby forming an iontophoretic (ion-pumping) galvanic couple. The second metal coating extends proximally from about the point of entry of the catheter into the vas to a location outside the body. Thus, the two metals forming the couple are exposed in different regions, and the antithrombogenic and antimicrobial properties occur in different regions. In another embodiment of the DeLaurentis et al. invention, the inside of the catheter is coated with two galvanically connected dissimilar metals, and the junction therebetween is located at a point sufficiently remote from the distal end so that it is ordinarily not reached by blood. The two dissimilar metals may include an oligodynamic metal such as silver and a more noble metal such as platinum. Stents, valves and artificial blood vessels as described by DeLaurentis et al. similarly include a junction of dissimilar metals, one of which may be oligodynamic metal and the other a more noble metal. In particular, the less noble or oligodynamic metal is located on that surface or surfaces of the device which, when in use, are adjacent to solid body tissue, while in all cases the more noble metal is adjacent the principal path for blood flow for thereby reducing clot formation.